1. Field of the Invention
This invention relates to a catheter for injecting a therapeutic composition to the diseased part in a living body, particularly to the ischemic region of the heart or the proximal part thereof.
2. Description of the Related Art
The patients of ischemic cardiopathy are increasing year after year owing to the growth of risk factors such as the inclination of eating habits toward the Western style and the aggravation of social stress. Particularly the increase of patients of serious heart failure has been posing a grave problem in advanced countries. Globally, 15 million new patients are occurring in a year.
As ways of curing such ischemic cardiopathy, studies on the gene therapy and the cell therapy have been under way. The conventional catheters which are applicable to such therapeutic methods are provided at the distal end portions thereof with an injection needle intended for injecting a therapeutic composition.
They are disclosed in U.S. Pat. No. 5,405,376 (corresponding to Japanese Unexamined Patent Publication No. Hei 8-508917) (Patent Reference 1), U.S. Pat. No. 5,797,870 (Patent Reference 2), U.S. Pat. No. 6,254,573 (Patent Reference 3), U.S. Pat. No. 6,309,370 (corresponding to Japanese Patent Laid-open No. 2001-87392) (Patent Reference 4), U.S. Pat. No. 5,972,013 (Patent Reference 5), U.S. Pat. No. 6,592,552 (corresponding to Japanese Unexamined Patent Publication No. 2001-516625) (Patent Reference 6), U.S. Pat. No. 5,931,810 (Patent Reference 7) and U.S. Pat. No. 6,102,887 (Patent Reference 8), for example.
Patent Reference 1 and Patent Reference 2 disclose catheters which are provided with a spiral injection needle. Patent Reference 3 and Patent Reference 4 disclose catheters which are provided at the distal end portions thereof with a contact-type sensor composed of a pressure sensor.
Patent Reference 5 and Patent Reference 6 disclose catheters which include a mechanism for creating a negative pressure in a catheter and consequently fixing the distal end portion of the catheter to a relevant tissue by virtue of suction. Patent Reference 7 discloses a puncturing device which is adapted to take hold of a relevant tissue mechanically, fix the distal end portion thereof to the tissue, and form a puncture aimed at.
Patent Reference 8 discloses a catheter which is provided with an injection needle held in the distal end portion thereof and a fixing device capable of radially opening from the distal end portion outwardly. Patent Reference 8 incidentally discloses a fixing device pointed in the leading terminal and a fixing device not pointed in the leading terminal both.
The spiral needle involved in Patent Reference 1 and Patent Reference 2 is such that, during the injection of a therapeutic composition, it is prevented from slipping out of the tissue and enabled to effect infallible injection. It is, however, not easily drawn out in the direction of extraction. While the spiral needle is stuck in a feeble cardiac muscle in the state of infarction, for example, an erroneous motion produced by the distal end portion of the catheter will possibly cause the spiral needle to tear off the cardiac tissue.
The contact-type sensor involved in Patent Reference 3 and Patent Reference 4 is disposed on the terminal face of the distal end portion of the catheter and, therefore, is required to contact the cardiac tissue without fail. Since the interior of the heart has a heavily irregular surface, the contact-type sensor tends to incur an error and entails the problem of lacking precision.
The catheter involved in Patent Reference 5 and Patent Reference 6 is aimed at being used in a flat region which is not filled with such humor as the blood. If it is applied to the surface of a tissue which is filled with the humor and is not invariably flat, therefore, it will incur difficulty in enabling the distal end portion of the catheter to contact perfectly closely to the surface of the tissue and will entail the possibility of aspirating the humor.
The puncturing device involved in Patent Reference 7 is directed toward taking hold of the heart sac which possesses comparatively appreciable strength. If it is applied to such a feeble tissue as the tissue of cardiac muscle in the state of infarction, for example, it will possibly rip off the tissue.
The fixing device with a pointed leading terminal which is involved in Patent Reference 8 is capable of keeping the catheter fixed to a tissue during the puncturing of the tissue and the injection of a therapeutic composition therein. It is, however, expanded radially after it has been stuck into the tissue aimed at. It, therefore, carries out a very large invasion on the peripheral part of the issue aimed at. The fixing device with no pointed leading terminal which is involved in Patent Reference 8 incurs extreme difficulty in inducing the catheter to operate and fails to fix the catheter at an arbitrary region in the heart because it fixes the catheter to the tissue by widening the columnar carneae in the heart.